Storage battery charging device



June 18, 1957 A. E. R. ARNOT 2,796,577

STORAGE BATTERY CHARGING DEVICE 1 Filed May 4, 1954 2 Sheets-Sheet 1Jar/2a 71115 J June 18, 1957 A. E. R. ARNOT 2,796,577

STORAGE BATTERY CHARGING DEVICE Filed May 4, 1954 2 Sheets-Sheet 2UnitedStates PatentO 2,796,577 STORAGE BATTERY CHARGING DEVICE AlfredErwin Reginald Arnot, Basingstoke, England, as-

.signor Emmanuel Kaye and John Reginald Sharp, both of Basingstoke,England 'Application'May 4, 1-954, SerialNo. 427,615 Claims priority,application Great Britain May 5, 1953 6 Claims, (Cl. 320-40 Thisinvention comprises improvements in or relating to storagebatterycharging devices. I

When storage batteries are being charged it is desirable to give thema-certain amount of overcharge, as is wellknown, but the overchargeshould not be excessive. Various devices have been suggested forautomatically allowing a .certain amount ,of overchargeand then cuttingoil the charging current, but these'devices as hitherto proposed, sufferfrom-various disadvantages. For example, an ampere-hour meter mounted ona stationary charger must be manually set to put the required number ofampere-hours of charge back into the battery, but the number ofampere-hours which have been discharged are not known and therefore thesetting cannot be accurate; it, to overcome this, an ampere-hour meteris mounted on a vehicle where it can measure the amount of discharge, ithas been found that the instrument cannot be made sufiicien-tly ruggedto withstand the shocks and vibrations to which it is subject. Anotherdevices comprises a relay set to the critical battery voltage, whichenergizes a time switch at this point of charge; the switch operates tocut off the charger at a pre-set time after it has been started. Thisdevice, although rather complex, is found to be satisfactory forstationary chargers, but the mechanism is not sufiiciently robust forchargers mounted on vehicles or otherwise subject to shocks orvibration.

I It is an object of this invention to provide a simpler and more robustdevice for the purpose in view.

The present invention comprises a batterycharging control device havingin combination contacts which can operate to cut oil battery chargingcurrent, means to set the contacts tor charging, means to operate thecontacts to out off charging which comprise athermally responsiveelement and means for applying heat to the said element dependent uponthe battery voltage so that after a time the element will respond andallow the contacts to operate to cut off charging current.

The means to apply heat to the said element dependent upon the batteryvoltage may conveniently consist of a resistance element which has anon-linear voltage characteristic so that it gets hot quickly as soon asthe voltage applied to it exceeds a critical amount. Such materials arewell known in the electrical art. One such material which isparticularly well-known is that sold under the trademark Thyrite, aceramic-like silicon carbide non-linear resistor material.

Preferably a variable resistance is included in series with theresistance element for the purpose of enabling the time of operation ofthe device to be pre-set. The thermally-responsive element may, forexample, consist of a block of readily-fusible metal and an element heldby said block from movement as long as the metal is in the solid state,but free to move when the metal is melted. Such elements are known perse, and any such device which has a suitable time delay as hereinafterexplained may be adopted according to the present invention. Preferably,the thermally responsive element and means for P" r 2,795,577 PatentedJune 18, 1 957 2 applying heat thereto are incorporated in athermally-insulated casing, for example thick solid cork material.

Conveniently the device according to the present invention includesmeans whereby after it has been operated and has cooled against-thecontact can readily be reset.

The following is a description by way of example of one construction ofbattery charging control device in accordance with the invention:

In the accompanying drawing:

Figure l is a plan of the device with the top cover removed,

Figure 2 is a section upon the line 2-,,-,-2 of Figure 1, and i Figure 3is a circuitdiagram showing ,a typical application of the device of theinvention.

The device comprises a receptacle ;11 which may be of cast metal or ofa' moulded plastic material and which has a cylindrical main portion andan enlarged hollow top portion 12 which is closed by a metal lid 13 heldin place by screws, The top portion 12 of the device is separated fromthe cylindrical portion 11 by .a-partition 14 so that the top portionconstitutes in effect a hollow box. The cylindrical receptacle 11' islined with thick cork 15, having a cylindrical interior which containstwo metallic terminal blocks 16,- 17 enclosed between cork pads 18, 19,Theterminal blocks 16, 17 are separated bya disc 20, made of thebefore-mentioned material; such as Thyrite, to provide a resistanceelement preferably having a non-linear voltage characteristic. Thepartition 14 contains an insulating bush 21 through which leads 46, 47-(Fig. 3) are taken down through the cork 15, one to the lower block 17'and ne to the upper block 16. The leads are secured to the blocks byscrews which do not appear in Figs, 1 and 2 as the section 2'2 on whichFigure 2 is taken is loo'liingthe other way. Current can therefore bepassed through the .disc 20 from one block to the other and the leadsare connected up through a variable resistance 42 to a battery 43 whichis being charged so that the battery voltage is applied to the disc 20.

The assembly of the blocks 1.6, 17 and disc 20 is held firmly togetherby a screw 22 which is insulated from the block 17 by an insulating bushand washer 23. The block 16 contains a cavity 24 which is partly filledwith an easily fusible alloy 25.

Dipping into the alloy is a square shaft of insulating material 26 whichpasses up through the cork disc 18 through a ,central aperture in thepartition 14 and fits into a ratchet wheelZ? .euppootedin a block 28moulded out of the same material as the partition 14 so that it standsup above the level of the partition.

The upper surface of the block 28 is groved out, as can be seen inFigure 1, to receive a push-rod 29. On the side of the push-rod there issecured a spring pawl 30 which is intended to engage the teeth of theratchet wheel 27. The slidable push-rod 29 is held down in the slot ofthe block 28 by a cap-plate 31 and screws 32. It carries a push buttonhead 33 which passes through the wall 12 of the upper part of thereceptacle, and it is urged in the outward direction by a spring 34. Theinner end of the push-rod 29 bears on the operating arm 35 of amicroswitch 36 secured inside the hollow top 12. The microswitch hasterminal screws 37, 38 (Figure 2) and leads 48, 49 (Fig. 3) connect thescrews 37, 38 to terminals on an insulating terminal block 40, seen inFigure 1. The leads 46, 47 which pass through the bush 21 are alsoconnected to terminals on the block 40 and an insulating bush 41 in thewall 12 permits leads 50, 51, 52, 53 (Fig. 3) to be taken into the topof the device and coupled as required to the terminals on the block 40.The leads 52, 53 which are connected via block 40 to leads 48, 49 andthe microswitch 36, are connected to suitable control means such asrelay 44 for a battery charger generator 45 so that when themicro-switch is closedthe charging circuit connecting battery 43 to saidgenerator. is completed and when the micro-switch is opened the chargingcircuit is broken.

In operation, assuming that it is desired to charge a battery to whichthe device is connected, the push-button 33 is pressed in. This closesthe micro-switch 36 and starts battery charging. When the pressure onthe pushbutton is taken away, the push-rod 29 and the button 33 remainpressed in because the pawl 30 engages one of the teeth of the ratchetwheel 27 and holds said push rod inwards against the pressure of thespring 34.

Charging proceeds, and the disc and any resistance elements put inseries with it in the circuit are so calculated that, under normalbattery voltage, very little current will pass between the blocks 17 and16, but as soon as the battery becomes fully charged and its terminalvolts rise substantially, the increased voltage applied to the disc 20is sufiicient to cause a very large increase in the current flow. Theconsequence is that the heating efiect of the current is much increasedand after a time the temperature of the block 16 rises to a point atwhich the easily fusible alloy melts. As soon as this occurs the shaft26 is free to rotate, the ratchet wheel 27 rotates with it under theeffort exerted by the spring 34 and thus the plunger 29 is withdrawnfrom the micro-switch 36 and the charging circuit is broken.

The parts are so proportioned and the resistance in series with theblocks'16, 17 is so chosen that the time which elapses between thebattery voltage rising and the release of the switch is adequate toafford a suitable amount of overcharge for the battery.

When the battery has been cut-out the block 16 containing the fusiblealloy 25 begins to cool down again, the alloy 25 solidifies, andthereafter, if the push-button is pressed in again, the chargingoperations can be repeated.

It will be seen that the device re-solidifies automatically after it hasbeen operated, it aifords a suitable degree of overcharge, it is shockand vibration proof and of exceedingly simple and robust construction.

The variable resistance 42 included in series with the blocks 16, 17enable the time of overcharge to be varied as required.

The contacts of the micro-switch 36 are preferably connected to aseparate relay 44 as shown for breaking the charging circuit.

I claim:

1. A battery charging control device having in combination contactsoperable to cut off battery charging current, means to set the contactsfor charging, means to operate the contacts to cut off charging whichcomprise a thermally responsive element, and means for applying heat tosaid element dependent upon battery voltage which comprise a resistanceelement which has a non-linear voltage characteristic so that it getshot quickly as soon as the voltage applied to it exceeds a criticalamount so that after a time the element will respond and allow thecontacts to operate to cut off the charging current.

2. A battery charging control device as claimed in claim 1, wherein avariable resistance is included in series with the resistance elementfor the purpose of enabling the time of operation of the device to bepre-set.

3. A battery charging control device having in combination contactsoperable to cut off battery charging current, means to set the contactsfor charging and means to operate the contacts to cut off charging whichcomprise a thermally-responsive element and a resistance element in heatconductive relation to the thermally-responsive element, the resistanceelement having a non-linear voltage characteristic so that it gets hotquickly as soon as the voltage applied to it exceeds a predeterminedvalue.

4. A battery charging control device as claimed in claim 3 having inseries with the resistance element a variable resistance which can beset to enable the time of operation of the control device to be varied.

5. A battery charging control device as claimed in claim 3, wherein-thethermally-responsive element consists of a block of readily fusiblemetal and an element held by said block from movement as long as themetal is in the solid state, but free to move when the metal is melted,the said element held by said block being operatively connected to thecontacts.

6. A battery charging control device as claimed in claim 3, wherein thethermally-responsive element consists of a block of readily fusiblemetal and a movable element held by said block from movement so long asthe metal is in the solid state, but free to move when the metal ismelted, the resistance element being located in heat-transferablerelation to said readily fusible metal and the combination of fusiblemetal, movable element and resistance element being enclosed in athermallyinsulated casing.

References Cited in the file of this patent UNITED STATES PATENTS729,323 Garrett May 26, 1903 937,332 Richardson Oct. 19, 1909 1,210,331Kuhn Dec. 26, 1916 1,500,268 Replogle July 8, 1924 1,507,300 ReplogleSept. 2, 1924 1,738,540 Replogle et al Dec. 10, 1929 2,012,903 BeetemAug. 27, 1935 2,286,340 Bulpitt June 16, 1942 2,314,863 Brown et al Mar.30, 1943

